Many diverse applications need to remotely determine the position of various objects. For example, researchers and managers of wild or domestic animals often need to know where animals are located. In addition, managers of fleets, whether of automobiles, trucks, rail cars, planes, or ships, need to know locations for their vehicles. In still other applications, the locations of balloons, buoys, and other platforms need to be remotely known from time-to-time. Preferably, the locations of such objects are reported as needed to a remote monitoring office. The remote position determination process incorporates two basic steps. Namely, the objects' positions are determined from time-to-time, and data describing those positions are communicated to the monitoring office.
Conventional remote position determination systems force their users to make difficult compromises. For example, researchers currently utilize a satellite-based remote position determining system operated by the Centre National d'Etudes Spatials (CNES, France), NASA, and the NOAA. Transmitters are placed on objects to be tracked, and compatible receivers are located on one or two orbiting satellites. The satellites record the transmitted signals they receive and later dump data describing these signals to a ground processing station for Doppler-based calculations which determine positions. While this system can determine locations at some very remote locations, it is expensive, inflexible, and unreliable. Moreover, it is available only for scientific research or experimental tracking, not for commercial applications. Consequently, only a small portion of the remote position determination needs are met.
In particular, the unreliability of this conventional system is due, at least in part, to the fact that transmitters engage in numerous unnecessary transmissions and thereby consume large amounts of electrical power and reduce the life of the transmitter. Moreover, the ability of only one or two overhead satellites to receive a transmitter's signal and the ability of the ground processing station to accurately resolve the transmitter's location are dubious at best. The satellites can track only transmitters which happen to be under their ground paths, and accurate position determination requires that the transmitted signal be received at a satellite for a duration of around 20 minutes. Furthermore, the ground processing station often takes several weeks to provide location data to a monitoring office. By the time that a monitoring office learns of a location, the location data are stale. The inflexibility is due, at least in part, to an inability to control the operation of the transmitter after it is in the field and the limited life of the batteries used by the transmitter. Often times, the power drain of transmitters permits them to remain operational for only a few weeks at best. The high cost is due, at least in part to the massive infrastructure which must be in place to support remote position determination.
Other remote position determination systems have been suggested. For example, one system suggests coupling a LORAN receiver with conventional cellular radiotelephones. The reliability of this system may improve upon the above-discussed satellite-based system in some ways, but reduce reliability in other ways. For example, this and similar systems would be operational only in locations where both LORAN signals can be received and where conventional cellular telecommunications are available. This limitation makes such a system inappropriate for many applications, such as those that require tracking over a broad area or those that require tracking in very remote areas. Moreover, the physical requirements for an antenna which receives LORAN signals make such a system inappropriate for applications requiring small physical size. Furthermore, the reliance upon two diverse systems, such as a LORAN positioning system and a cellular telecommunication system, increases complication and cost while proportionately increasing unreliability, weight, and power consumption.